The objective of research and development in the field of illumination light source of this century is to use a light emitting diode (LED) to produce a white light having a similar hue of sunlight to replace the white-light illumination of traditional fluorescent lamps. At present, single-chip white-light LED technology promoted all over the world primarily uses a blue-light LED chip that emits a wavelength of 440 nm˜460 nm by exciting a yellow-light phosphor to produce white light. The method features the advantages of simple manufacturing process and low cost, but the white light produced by the method has the disadvantages of poor color saturation and color rendering.
In recent years, ultraviolet light emitting diode (UV-LED) chip that emits a wavelength of 360 nm˜400 nm is used for exciting phosphors of three different colors: red (R), green (G) and blue (B), and these three colors can be mixed to form white light. The method features the advantages of high light emitting efficiency and color rendering as well as the UV-LED chip can work with various different phosphors, but the method has the disadvantages of damaging the products under the exposure of UV light for a long time and reducing the life expectancy of the chip, since the UV light has a short wavelength and the released energy is much higher than that of blue light or green light. In addition, it is necessary to mix several types of phosphors appropriately to control the quality of the white-light light source, and thus the research and development of the foregoing method and technology uses UV light to excite a single phosphor to produce white light, and the industrial value derived from such method and technology are immeasurable.
In the prior art, an alkaline-earth silicates compound is used as the main material, and phosphors applicable for the excitation of blue light or UV light have been disclosed in many issued patents including OSRAM's U.S. Pat. No. 6,812,500, General Electric's U.S. Pat. No. 6,621,211 and Toyota Gosei's U.S. Pat. No. 6,809,347, etc.
However, the foregoing patents come with a light emitting activator selected from a bivalent europium (Eu2+) for radiating yellow-green as well as yellow to orange lights under the excitation of blue light or UV light. At present, there is no alkaline-earth silicates compound related patent that produces white light by exciting a phosphor material with UV light yet.
In addition, a patent related to the phosphor material of A2-2xNaxExD2V3O12 as disclosed in General Electric's EP Pat. No. 1,138,747 similarly excites a single phosphor by UV light, but such patent selects a vanadates compound for the phosphor material.